Oil palms, which are plants that grow in tropical zones including Malaysia, are crops for the production of oils. The cultivation areas for oil palms have fast expanded.
In particular, recently, the cultivation areas thereof have sharply extended to Mexico as well as Africa. As the areas for oil palms have extended to South China, the cultivation areas and the use thereof are becoming larger than canola as well as soybeans, which are legumes.
Oil palms are processed by milling to obtain oils. Herein, during the milling process, much steam is introduced, thereby generating condensed water with a high temperature of about 80° C. And, since it is compressed at a high pressure in the oil milling process, water contained in plants also flows out, so that large amounts of solid contents are discharged as the process water.
However, there is no proper method for processing such process water since the process water is discharged at a high concentration. For this reason, so far, most palm oil mill factories have been using illegal discharging methods in combination with a method of naturally evaporating the process water using ponds. However, these methods are causing immense problems such as air pollution as well as serious soil pollution and water pollution, so it can no longer be ignored.
Furthermore, in addition to the final effluent (POME) which is discharged from the palm oil milling process, palm by-products such as palm oil decanter cake (PODC), palm kernel shell (PKC), palm kernel cake (PKS), etc. are produced in the palm oil milling process. Such substances have been used as fuel for existing mill factories to produce steam. However, since these substances are voluminous and hard to process, there are many problems.
For the technique for processing palm oil mill waste, “Method for Preparing Biofertilizer Using Palm Oil Mill Wastage” (Korean Patent No. 10-0938490; Patent Document 1) introduces a process of carbonizing kernel shell, incinerating EFB, treating POME with micro air bubbles and filtering the treated POME to obtain decanter cake, mixing them, and maturing the mixture to produce a biofertilizer.
However, the above technique has a problem that since kernel shell, fruit bunch, etc. are carbonized and incinerated, respectively, the consumption of energy sources occurs accordingly.
In addition, the above technique does not provide a method for processing palm kernel cake or palm oil decanter cake, etc. out of the by-products.
As such, up to now, not only it is very difficult to process final palm oil milling process water, but also the process water cannot be processed by existing water treatment methods; thus, a method of allowing the process water to sequentially remain in dozens of large ponds for a long time (about 60 to 120 days) to evaporate it or illegally releasing the process water has been taken. However, the process water heavily decays, which causes the occurrence of an offensive odor, resulting in air pollution, etc.
In particular, the method of converting the generated final palm oil process water into waste water and processing it using ponds (Ponding process) has problems in that it requires large areas of land and is difficult to control, and that deposited substances should be removed continuously every year. Recently, in Europe, techniques of producing biogas have been introduced. However, it takes long time for the digestion to produce biogas, and the amounts of the produced biogas are not constant. Also, even if some biogas is produced, since the waste water finally discharged after producing the biogas contains a high concentration of nitrogen, the cost for processing the waste water is huge. For this reason, these techniques have not been widely used yet, and most of the techniques have failed and have not come close to practical use.
Furthermore, it is hard to process the PODC because its production amounts are large and the water contents are high. Thus, a method of fermenting the PODC to produce a fertilizer has been used. The PKS has been used as fuel, but there is difficulty in obtaining economic efficiency because the water contents and the volume are large. The PKC has been partly used as feed resources, but this could not be a long-term treatment method because of the difficulty in marketability due to changes in quality, etc. Consequently, these substances are just released in large areas of open-air yards. Accordingly, there are many difficulties in solving such problems.